1. Field of the Invention
The present invention relates to an apparatus and a method of forming images on both sides of a recording medium.
2. Discussion of the Background
Image forming apparatuses, such as copying machines, printers, facsimile machines, etc. are known to form images on both sides of a recording medium (hereinafter sometimes referred to as a sheet). Such image forming apparatuses capable of recording images on both sides of a sheet generally transfer an image of one side of an original, which has been formed and visualized on an image bearing member, onto one side of a sheet, and fix the image onto the sheet by a fixing device. The sheet is then reversed by a reversing path and is conveyed again so that an image of the other side of the original, which has also been formed and visualized on the image bearing member, is transferred and fixed onto the other side of the sheet.
In the above-described image forming apparatuses, because the sheet conveying direction has to be reversed, a sheet tends to be curled when an image is fixed onto one side of the sheet and reliability of sheet conveyance is hard to obtain.
Japanese Patent Laid-open Publications No. 1-209470, No. 3-253881 and No. 10-142869 disclose an image forming apparatus in which toner images, which have been transferred onto both sides of a sheet from a first image bearing member and a second image bearing member, respectively are fixed at one time.
When forming images on both sides of a recording medium, positions of the images on the front side and the back side of the recording must coincide with each other. For example, when sheets having character images on both sides thereof are bound to be a book, if the positions of respective character images on the front and back sides of each sheet are deviated from each other, the heights of respective lines in the character images in the right side and left side pages do not coincide with each other when the book is opened. This causes difficulty in reading the book and makes the appearance of the book unattractive. This can be said not only for character images but also for graphic images. Further, even in a single sheet having images on both sides thereof, when the images are character images and when the sheet is thin such that the characters on the back side are readable from the front side, if the positions of respective images on the front and back sides of the sheet are deviated from each other, it is hard to read the characters.
In some background image forming apparatuses that form images on both sides of a sheet, slippage of a transfer belt causes deviation in the positions of the images on both sides of a sheet, thereby deteriorating the quality of the images.
Japanese Patent Laid-open Publication No. 11-327254 describes a technology for preventing color deviation in forming a color image. The technology relates to a method of causing positions of a plurality of images of different colors, which are to be superimposed with each other on a same surface of a sheet, to coincide with each other, but does not relate to a method of causing positions of the images on both sides of a sheet to coincide with each other.
Accordingly, one object of the present invention is to address the above-discussed and other problems.
Accordingly, preferred embodiments of the present invention provide an image forming apparatus and an image forming method that precisely set the image positions on both sides of a recording medium. According to a preferred embodiment of the present invention, an image forming apparatus includes a first image bearing member; a second image bearing member; a positioning mark forming device configured to form a positioning mark on the second image bearing member; and a positioning mark detecting device configured to detect the positioning park formed on the second image bearing member. A first side visual image formed on the first image bearing member is transferred onto the second image bearing member for transferring from the second image bearing member onto a first side of a recording medium. A second side visual image formed on the first image bearing member is transferred from the first image bearing member onto a second side of the recording medium, so that the first and second side visual images are obtained on the first and second sides of the recording medium, respectively. When forming the first side and second side visual images on the first and second sides of the recording medium, an image forming operation is controlled according to detection of the positioning mark with the positioning mark detecting device such that positions of the first side and second side visual images on the first and second sides of the recording medium coincide with each other.
In the above-described image forming apparatus, writing of the second side image on the first image bearing member, or conveyance of the recording medium, may be controlled according to the detection of the positioning mark with the positioning mark detecting device, such that positions of the first side and second side visual images on the first and second sides of the recording medium coincide with each other.
Further, when forming one of the first side and second side visual images on the recording medium, the conveyance of the recording medium may be controlled according to the detection of the positioning mark with the positioning mark detecting device such that a leading edge of one of the first side and second side visual images is placed at a predetermined position on the recording medium. Alternatively, when forming one of the first side and second side images on the recording medium, formation of the positioning mark on the second image bearing member may be omitted.
Further, the above-described image forming apparatus may include a fixing device, and the first side and second side visual images transferred onto the first and second sides of the recording medium may be fixed onto the recording medium, respectively, by the fixing device in a state that the second image bearing member and the recording medium are overlapped with each other.
Furthermore, the above-described image forming apparatus may include an exposure device configured to form a latent image of an image on the first image bearing member; a developing device configured to visualize the latent image formed on the first image bearing member into a visual image; and a transfer device configured to transfer the visual image from the first image bearing member onto the second image bearing member. In this case, a latent image of the positioning mark is formed with the exposure device on the first image bearing member and is developed to a visual image of the positioning mark with the developing device, and the visual image of the positioning mark is transferred from the first image bearing member to the second image bearing member with the transfer device, thereby forming the positioning mark on the second image bearing member.
Still furthermore, the above-described image forming apparatus may include a positioning mark cleaning device configured to remove the positioning mark formed on the second image bearing member. In this case, when the second image bearing member is formed as an endless belt, the positioning mark cleaning device is placed downstream of the positioning mark detecting device in a vicinity thereof in a rotating direction of the second image bearing member formed as the endless belt.
Furthermore, in the above-described image forming apparatus, the positioning mark may be formed at a position outside of an image forming area on the second image bearing member with respect to an image width direction.
Furthermore, a color of the positioning mark may be different from that of a surface of the second image bearing member. In this case, the image forming apparatus may include a positioning mark developing device configured to visualize the positioning mark in a color different from that of the surface of the second image bearing member.
Alternatively, a color of the surface of the second image bearing member may be different from that of the first side visual image transferred from the first image bearing member. When the positioning mark is formed on a part of the second image bearing member at one side thereof at a position outside of an image forming area in an image width direction, a surface of the part of the second image bearing member at one side thereof where the positioning mark is formed may be formed in a color different from that of the first side visual image transferred thereupon from the first image bearing member.
Furthermore, in the above-described image forming apparatus, the positioning mark may be formed at a position outside of an area corresponding to a maximum size of the recording medium on the second image bearing member.
Still furthermore, in the above-described image forming apparatus, the positioning mark may be formed at a position in front of the first side visual image on the second image bearing member.
Further, the above-described image forming apparatus may include a cooling device configured to circulate air to cool the second image bearing member. In this case, the cooling device is not operated when at least one of the positioning mark and the first side visual image on the second image bearing member passes a cooling area of the cooling device.
Furthermore, in the above-described image forming apparatus, the second image bearing member may be formed as an endless belt and arranged so as to extend in a vertical direction. In this case, the positioning mark detecting device is placed such that a sensing surface thereof is substantially in parallel with a surface of the second image bearing member formed as the endless belt.
Further, the image forming apparatus may include a cleaning device configured to clean the second image bearing member, and the cleaning device may remove the positioning mark formed on the second image bearing member.
According to another preferred embodiment of the present invention, an image forming method for obtaining a first side visual image and a second side visual image on a first side and a second side of a recording medium by transferring the first side visual image from a first image bearing member to a second image bearing member and from the second image bearing member onto the first side of the recording medium, and transferring the second side visual image from the first image bearing member to the second side of the recording medium includes the steps of; forming a positioning mark on the second image bearing member; detecting the positioning mark; and controlling formation of the second side visual image according to the detection of the positioning mark on the second image bearing member such that positions of the first side and second side visual images on the first and second sides of the recording medium coincide with each other.